ABSTRACT
Abstract Three c o m m e r c i a l l y u s e d accelerat ing mater ia ls , c a l c i u m ch lo r ide , c a l c i u m nitrate a n d s o d i u m thiocyanate , w e r e s t u d i e d for their effects o n the h y d r a t i o n of a pa r t i cu la r o r d i n a r y P o r t l a n d cement. Tes t ing was ca r r i ed ou t at equa l w e i g h t percentage levels o n cement pastes at a wa tencemen t ra t io o f 0.50. Test procedures u s e d w e r e X - r a y dif f ract ion, different ial s cann ing ca lo r imet ry , s o l u t i o n analysis , semi-adiabat ic a n d semi-i so thermal ca lor imet ry . Resul ts genera l ly agreed w i t h the k n o w n effects of the three admix tu res i n site pract ice w i t h the c a l c i u m ch lo r ide b e i n g effective at a l l ages, the c a l c i u m nitrate at ea r ly ages a n d the s o d i u m thiocyanate at later aees. There w a s also a g o o d correspondence be tween the results ob ta ined w i t h tne va r ious test me thods e m p l o y e d . S ign i f i can t depressions of the levels of h y d r o x i d e a n d sulphate ions i n so lu t ion i n the first three hour s we re f o u n d , p a r t i c u l a r l y w i t h the c a l c i u m salts. Dep re s s ion of the su lpha te i o n concent ra t ion w a s pa ra l l e l ed b y the fo rma t ion o f g y p s u m i n the ear ly age X - r a y di f f ract ion a n d different ial s cann ing ca lo r ime t ry studies. T h e effects of the anions present i n the admix tu res appear to be s ignif icant i n the later stages of h y d r a t i o n out no clear mechan i sms we re iden t i f i ed . K e y - w o r d s : Acce le ra tors , H y d r a t i o n , S o l u t i o n C h e m i s t r y , Sulpha te , H y d r o x i d e , P o r t l a n d Cemen t .
